The present invention relates to meltblown fiber webs and, in particular, to multicomponent meltblown fiber webs and laminates thereof.
Multicomponent spunbond fibers refer to fibers which have been formed from at least two polymer streams but spun together to form a unitary fiber. The individual components comprising the multicomponent fiber are usually different polymers and are arranged in distinct zones or regions that extend continuously along the length of the fibers. The configuration of such fibers can vary and commonly the individual components of the fiber are positioned in a side-by-side arrangement, sheath/core arrangement, pie or wedge arrangement, islands-n-sea arrangement or other configuration. Multicomponent fibers and methods of making the same are known in the art and, by way of example, are generally described in U.S. Pat. No. 5,344,297 to Hills; U.S. Pat. No. 5,336,552 to Strack et al. and U.S. Pat. No. 5,382,400 to Pike et al.
Generally, methods for making spunbond fiber nonwoven webs include extruding molten thermoplastic polymer through a spinneret, quenching the filaments and then drawing the quenched filaments with a stream of high velocity air to form a web of randomly arrayed fibers on a collecting surface. As examples, methods for making the same are described in U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 4,340,563 to Appel et al. and U.S. Pat. No. 3,802,817 to Matsuki et al. However, meltblown fabrics comprise a class of melt formed nonwoven fabrics which is distinct from those of spunbond fiber webs. Meltblown fiber webs are generally formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, air streams which attenuate the filaments of molten thermoplastic material to reduce their diameter. Thereafter, the meltblown fibers are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Meltblown fiber processes are disclosed in, for example, U.S. Pat. No. 3,849,241 to Butin et al.; U.S. Pat. No. 5,160,746 to Dodge et al.; U.S. Pat. No. 4,526,733 to Lau; and others. Meltblown fibers may be continuous or discontinuous and are generally smaller than about 10 microns in average diameter. In addition, meltblown fibers are generally tacky when deposited onto a collecting surface or other fabric.
Multicomponent meltblown fibers have been made heretofore. As an example, multicomponent meltblown fibers have been made to form a thermally moldable face mask such as, for example, as described in U.S. Pat. No. 4,795,668 to Krueger et al. Similarly, European Patent Application No. 91305974.4 (Publication No. 0466381 A1) teaches a conjugate meltblown fiber web suitable for thermally molding to the shape of a filter cartridge. In addition, U.S. Pat. No. 5,935,883 to Pike describes split multicomponent meltblown fibers and laminates thereof suitable for use in filter applications, wipers, personal care products and other uses.
However, there exists a need for multicomponent meltblown fiber webs which can be utilized to provide nonwoven webs and laminates thereof with varied structures and/or improved physical properties such as softness, strength, uniformity, peel strength and/or controlled barrier properties. Further, there exists a need for efficient and economical methods for making the same.
The aforesaid needs are fulfilled and the problems experienced by those skilled in the art overcome by nonwoven webs of the present invention comprising fine multicomponent fibers having a first polymeric component and a second polymeric component positioned in distinct zones within the fiber""s cross-section and which extend substantially continuously along the length of the fibers. The randomly interlaid web of extruded multicomponent fibers have an average fiber diameter less than 7 micrometers and comprise a first olefin polymer component and a second amorphous olefin polymer component. In one aspect, the first polymeric component comprises a crystalline propylene polymer and the second polymeric component comprises an amorphous propylene polymer. Further, the nonwoven web may have a hydrohead in excess of 50 mbar and a Frazier air permeability in excess of 100 cubic feet/minute/square foot.
In a further aspect of the present invention, nonwoven web laminates are provided comprising (i) a first nonwoven web of multicomponent fibers having a first polymeric component and a second polymeric component in distinct zones across the cross-section of the fibers which extend substantially continuously along the length of the fibers, said multicomponent fibers having an average fiber diameter less than about 7 micrometers; (ii) a second nonwoven web of continuous fibers having an average fiber diameter greater than about 10 micrometers; and (iii) a third nonwoven web of continuous fibers having an average fiber diameter greater than about 10 micrometers wherein the first layer is positioned between the second and third layers and further wherein the multilayer laminate has a hydrohead of at least 50 mbars, a Frazier air permeability in excess of 70 cubic feet/minute/square foot and cup crush energy of less than about 2150 g-mm. Desirably, the first layer comprises a meltblown fiber web and the second and third layers comprise spunbond fiber layers. In still a further aspect, the multilayer laminate may further comprise a fourth layer, such as a monocomponent meltblown fiber web, which is adjacent the first layer and also positioned between the second and third layers.